ENGELMANN THE ACORNS AND THEIR GERMINATION. I9I 



In all the Black-oaks which I could study the caulicle is longer 

 than the stalks. Thus in Quenus fiigra, imbricaria, pumila and 

 Kelloggii I find it twice as long ; in Q. coccinea and tinctoria^ rubra, 

 ilicifolia and agrifolia, it is three to four times as long. Q. densifiora 

 of the section Androgyne is similar in this respect to the first. 



A few White-oaks resemble the Black-oaks in the proportion 

 of these parts. These are Q. ?nacrocarpa and undulata* and espe- 

 cially Q. Robiir of Europe. In this and in the Californian Q. chry- 

 solepis I find the caulicle nearly three times longer than the stalks ; 

 in both of them I also notice the plumule unusually developed. 



But in the majority of White-oaks the caulicle is shorter than 

 the stalks of the cotyledons; I have seen it in the American J^. 

 alba, stellata, Gatrya?ia, Douglasii, Breweri, Prinus, Miihlenhergii, 

 prinoides, Michauxii, bicolor, duinosa^ pungens* and in Q. occidentalis 

 of southwestern Europe. It is very interesting to find that in the 

 hybrids of ^. mactocarpa and alba, which externally resemble 

 more the former than the latter, the proportion of the stalks- and 

 the caulicle is entirely that of the latter and not of the former. I 

 have observed this fact in hybrids from Illinois ( Hall) as well as 

 from Vermont {Pr ingle). 



By far the longest stalks or petioles, however, are found in ^. 

 virens ; in this species not only the cotyledons, as is well known, 

 but also their stalks, are coalescent : the caulicle itself is very 

 short, only about one-fourth or one-fifth the length of the stalks, 

 and the place where they separate from the caulicle is indicated 

 by the very small and imperfect plumule, completely imbedded 

 within the connate base of the stalks. 



The acorns of all oaks germinate in or on the ground, the 

 thickened stalks and the caulicle elongate ; the former become 

 2 to 4 or nearly as much as 6 lines long, while the cotyledons 

 themselves remain enclosed in the cracked seedshell, and from 

 between the bases of the stalks- the plumule grows up into the 



* All Colorado forms of ^ imdulata which I have examined, those with large and 

 •deciduous leaves vars. Gamhelii, Guiinisoni, yamesit, as well as the small- and spiny- 

 leaved form from the edge of the canon of the Arkansas, which I had considered .is identi- 

 cal with ^.pungens, have short stalks, while the pale and usually persistent-leaved forms 

 from Arizona, the true ^. pungens of Liebmann, have the stalks longer than the caulicle. 

 Finding the proportions of these parts to be constant and as indicating specific difference, 

 I am now inclined to consider ^. pungent, including ^. grisea as a distinct species, pro- 

 vided other chara- ters can be found to confirm this view. In a few acorns of this form I 

 have seen the cotyledons adhering together, but in the majority they were free. 



